Optically variable one-way mirror



SEARCH ROON QR 3&2809701 Oct. 25, 1966 J. F. DONNELLY ETAL 3,230,701

OPTICALLY VARIABLE ONE-WAY MIRROR 5, 1961 2 Sheets-Sheet 1 OriginalFiled Sept.

/5 26 24 2a l Z /20 K/CHAR'D C. COOPfR BY United States Patent 2 Claims.(CI. 83-77) This application is a divisional application of the parentapplication now abandoned entitled Mirror For Vehicles, filed September5, 1961, Serial No. 135,982 by John F. Donnelly and Richard C. Cooper.

This invention relates to mirrors, especially rear view mirrors forvehicles, and more particularly to mirrors having variable opticalcharacteristics.

It is well-known to every automobile driver that clear observance ofpedestrians, bicycle riders, and other vehicles depends to a greatextent upon the characteristics of his rear view mirror. Since thissmall item is relied upon so heavily, its optical characteristics shouldbe completely dependable in all types of surroundings normallyencountered. These varying surroundings include a great variety oflighting variations and traffic conditions. Any one of such lightvariations, e.g. glare of bright lights of a following automobile,bright sunshine, blackness of night, evening twilight, or the like, maybe coupled with any of many traffic conditions such as bumperto-bumpertraflic, presence of many pedestrians and bicycle riders, crossing ofdark intersections, multi-lane interweaving traffic, and so forth.

Heretofore, efforts have been expended to aid the driver by producingrear view mirrors capable of reducing glare, eg with tinted mirrors; orcapable of adapting to alternate darkness and bright lights, e.g. thetwo or three position, mechanical flip-flop mirrors. Such de vices arecertainly useful, but do not cause mirrors to be capable of adapting toall types of situations. Consequently, there has existed a great needfor a mirror allowing the control of the reflectivity of brightness overa wide range of values to accommodate the particular opticalcharacteristics of the situation.

Another design limitation encountered with present mirrors is that anyincrease in the dimensions of the mirrors to enlarge the rear visioncauses a proportionate decrease in the forward vision by enlarging theblind spot caused by the mirror. There exists a need for a mirrorsubject to driver-control to provide improved rear vision withoutcausing a larger blind spot. This mirror should also have a variablereflectivity to accommodate various lighting conditions as well asvarious traflic conditions.

It is therefore an object of this invention to provide a mirror thatsolves the above cited problems to increase the safety of drivers,pedestrians, bicycle riders and others. The invention provides a mirrorthat has variable optical characteristics capable of adjustingautomatically, or subject to driver control to adjust to lightingvariations and trafiic variations encountered.

It is another object of this invention to provide a mirror structurethat enables a very large rear view mirror to be used in vehicles sincethe blind spot in forward vision may be removed at the drivers desire.The invention provides a mirror in which the inconsistentcharacteristics of transparency and reflectivity may be alternated. Themirror may include both features of reflectivity brightness andalternate variable transparencyreflectivity, and thus is completelyadaptable to varying lighting conditions and traflic conditions.

These and other objects of this invention will be 3,280,701 PatentedOct. 25, 1966 apparent upon studying the following specification inconjunction with the drawings, in which:

FIG. 1 is a fragmentary elevational view of one embodiment of theinventive rear view mirror mounted adjacent of an automobile windshield;

FIG. 2 is a side sectional elevational view of one form of the firstembodiment of the inventive mirror;

FIG. 3 is a side elevational sectional view of a modified and secondform of the first embodiment;

FIG. 4 is a side elevational sectional view of a further modified andthird form of the first embodiment of the mirror;

FIG. 5 is a fragmentary elevational view showing the second embodimentof the novel rear view mirror mounted in an automobile and being in itstransparent state;

FIG. 6 is a fragmentary elevational view of the mirror as illustrated inFIG. 7 in its reflective state;

FIG. 7 is an enlarged front elevational view of the mirror illustratedin FIGS. 5 and 6 and showing in more detail the structure thereof;

FIG. 8 is a side elevational sectional view of the mirror as illustratedin FIG. 5, and taken on plane VIII- VIII;

FIG. 9 is a side elevational sectional view of the mirror as illustratedin FIG. 6, and taken on plane IX]'.X; and

FIG. 10 is a side elevational sectional view of a third embodiment ofthe invention as possessing the combined features of the first twoembodiments.

Basically, this invention comprises a mirror, especially an automobilerear view mirror, having variable optical characteristics. The mirrorincludes adjacent the reflective surface a layer having a variabletransparency responsive to an energy potential applied. In oneembodiment of the'invention, the variable transparency (i.e. variableopacity) substance is in front of the reflective mirror surface, and ispreferably variable in color, to cause variations in light reflectancefrom the mirror surface.

In a second embodiment of the invention, the variable transparency orvariable opacity substance is behind a one-way mirror surface such thatsaid mirror is transparent when said substance is transparent and isreflective when said substance is relatively opaque.

In the third form of the invention, the mirror includes a variabletransparency substance in front of the refiective surface to allowcontrol of the reflectivity brightness, and a variable transparencysubstance behind the surface to allow the mirror to be adaptable tovarious types of lighting and traffic conditions.

FIRST EMBODIMENT Referring now to FIG. 1, in the form of the inventionthere illustrated, mirror 10 is mounted adjacent the windshield 12 andabove the dashboard 14 of an automobile as by attachment to the top 'ofthe windshield frame. The mirror 10 includes reflecting surface 16, amounting means 18 and a suitable frame 15 as desired. The reflectingsurface 16 has a variable brightness reflectivity depending upon thelighting conditions involved. This is preferably accomplished bychanging the color of a substance adjacent the reflecting surface, suchthat glare will be filtered out, but only suflicient filtering willoccur to remove objectionable light without causing poor re solution ofthe object lines. This change is responsive to an energy potentialapplied to the mirror. The energy may be in the form of light, heat, orelectrical potential. The heat may be radiant, conductive, or created inthe mirror by converted light. The mirror includes a substanceresponsive to the particular form of energy used to vary intransparency, i.e. in opaqueness. Such colorchanging substances areoften called phototropic in the art. This invention, however, may in itsbroadest aspects utilize materials not normally termed phototropic. Forexample, in the second embodiment of this invention, materials changingin opacity by converting from a sol to a gel state and visa versa, maybe used as well as colorchanging materials. I.e., the particularsubstances used in the variable reflectance mirror may be varied as wellas the concentration thereof and the type and amount of energy appliedto produce the desired mirror.

FIRST FORM OF FIRST EMBODIMENT In the first structure of the inventionillustrated in FIG. 2, a transparent plate made e.g. of glass supports aconventional mirror surface 22 formed of a deposited metal film such asaluminum, chromium, silver, etc. in a conventional manner. Light raystransmitted to the glass 20 will thus reflect from surface 22 backthrough the glass 20 again. The color changeable material may beembodied in layer 24 sandwiched between glass layer 20 and a secondglass layer 26. The color changing material could be a dye which willreversibly change color when subjected to light energy, for example.Such dyes would include victoria blue, brilliant green, crystal violet,malachite green, luco bases of pararosaniline and others. One method ofobtaining the film to form this layer is to add one part of victoriablue and one part of malachite green to approximately 200 parts of hotwater, and preferably add one part of potassium cyanide as a catalyst ofthe reversing action. The precipitation resulting from this mixture isfiltered and washed with hot water containing potassium cyanide. It maythen be dissolved in 20 parts of an 85% methyl alcohol aqueous solution.To this added 10 parts of polyvinyl butyraldehyde acetal and 3 parts ofpolyglycol butyl ether. A film is then formed of this material bypouring it upon a flat surface and drying. This film is sandwichedbetween the glass plates 24 and 26. Suitable seals 28 and 30 may beprovided on the top and bottom and on the ends of the mirror inside theframe. The resulting mirror is reversibly activated by light. I.e. asthe light intensity increases, the color of the mirror gradually changesfrom a very light and almost colorless shade to a dark bluish-green.Thus, for example, if driving at night, the rear view mirror remains alight color to allow clear vision behind. When an automobile with brightlights follows closely, the intensity of the lights will cause themirror to respond and become darkened to the proper extent to filter outundesirable glare. Such a mirror is calibrated previously to respond tothe various light intensity levels and give the proper reflectivitybrightness.

Instead of the mixture of malachite green and Victoria blue dyestuffsmentioned above, only malachite green may be used if desired andprepared substantially as follows: 1 part of malachite green isdissolved in approximately 90 to 100 parts of water. A small amount ofpotassium cyanide catalyst is added. The precipitate resulting isfiltered off and washed with hot water containing potassium cyanide.This precipitate is dried and three parts of it are dissolved in asolution of parts polyvinyl butyraldehyde acetal, 50 parts of methylalcohol and 10 parts of diac'etone alcohol. Again, this material ispoured out upon a fiat sheet and dried to form a film. It is thensandwiched between glass plates. The resulting product actssubstantially as the one described above but possesses different colorhues.

Instead of forming an independent film and then sandwiching it betweenglass plates, it may be desired to form the film directly upon the faceof one of the glass sheets. Alternatively, other transparent materialsbesides glass may be used in certain instances, such as polymethylmethacrylate. Also, instead of the polyvinyl butyraldehyde acetal resinmentioned above to form film matrix for the light responsive material,other resins may be SECOND FORM OF FIRST EMBODIMENT Instead of themirror being automatically responsive to incident light, as with theheadlights of a following automobile, it may be desired to provide avariable reflectivity mirror controllable by the driver at hisdiscretion. Referring to FIG. 3, mirror 31 includes glass plate 33 withreflecting mirror surface 32 on the back. The bottom of the mirror issealed at 34 as are both ends (not shown) to form a chamber 36 betweenglass plate 33 and glass plate 38. This chamber may be filled with asuitable liquid, light-responsive, color-changing material. A plug 40 atthe top of a light-transmitting mate rial may be used to close thechamber. Mounted adjacent the mirror is a high intensity energy source42. The color-changing liquid in chamber 36 is calibrated to beresponsive only to this energy source. Such a liquid might, for example,be a solution of potassium ferrocy anide containing a small amount ofphenolphthalein indicator. Such an aqueous solution is yellow in thedark or when exposed to low light intensity, but gradually becomes darkpink when exposed to light of increasing intensity. The yellow colorreturns when the solution is again placed in the dark. By using a dilutesolution of potassium ferrocyanide, such a material will not besensitive to lights of approaching automobiles or daylight but may beclosely regulated with the high intensity source 42. A conventionalrheostat may be used to vary the electrical power to source 42 to enablethedriver to control the light intensity and provide a range of colorshades in chamber 36. This allows control of the reflectivity brightnessfrom mirror surface 32. Instead of liquid, a solid film as describedpreviously may be used here also.

Instead of the particular light-responsive substance mentioned, asubstance responsive to heat or temperature changes may be utilized.Thus, by making source 42 a radiant heat source, color control could bemaintained. An example is a solution of cobalt chloride container 6waters of hydration dissolved in ethyl alcohol, and containing a smallamount of water to control the pink-toblue color change point. Such asolution is obtained by the addition of 8 grams of cobalt chloride tocc. of ethyl alcohol having a specific gravity of about 0.8. The amountof water may be approximately 10 cc., but can be varied say from 5 to 15cc. to control the color change point. Upon energizing source 42, toapply radiant heat to this solution, the material will change from lightpink to a bluish color. The cobalt chloride solution may be embodied ina resin matrix by adding polyvinyl butyraldehyde acetal and drying to afilm. This can be sandwiched between glass sheets as indicatedpreviously.

Instead of applying radiant heat directly to these heat ortemperature-responsive materials, a light source may be used, incombination with a separate substance embedded in the film or dissolvedin the solution which is capable of converting light to heat. Examplesare various ferrous compounds, nickel salts, or cobalt salts, as well ascertain organic materials, e.g. ferrous sulfate, ferroammonium sulfate,and nickel sulfate.

THIRD FORM OF FIRST EMBODIMENT The structure illustrated in FIG. 4employs a pair of electrical elements on opposite sides of thecolor-changing material layer. In this arrangement, a glass containerhaving a back portion 50, a bottom portion 52, a front portion 54, andsuitable end seals (not shown) define a chamber 56 into which a liquidlight-responsive material may be placed and enclosed by a suitable cap58. Mirror surface 60 is coated on one side of the chambet to thus servealso as an electrode, providing the liquid used does not attack it. Onthe opposite side of the chamber is a second electrode 62 which must betransparent to allow light to pass through glass layer 54, throughsolution 56, reflect from mirror surface 60, and pass back through layer54. This electrode may for example, be a film of tin oxide, cadmiumoxide, antimony oxide, cobalt oxide, zinc oxide, indium oxide, titaniumoxide, chromium oxide, platinum oxide, or any other suitabletransparent, conductive film. Any of the oxides may be prepared by usingthe bromide, chloride or acetate of the corresponding metal.

If the mirror surface 60 is not resistant to the particular substance inchamber 56, a second conductive coating like 62 may be coated in theplace of mirror surface 60, with the mirror surface being coated on theoutside surface 66.

The electrical potential applied across the elements is supplied throughleads 68 and 70 from a suitable power source such as battery 72controllable through a variable resistor 74. An example solution in thechamber is a 0.1 normal solution of sodium chloride, slightly acidifiedwith hydrochloric acid, and having added thereto a few drops ofphenolphthalein indicator. With the electrodes approximately 3 mm.apart, a potential of approximately 0.9 volt causes the solution to turnpink. The pink color deepens upon an increase in the potential applied.By lowering the potential again, the color lightens. This reversibleaction is probably due to a change in the pH of the solution in responseto the applied. Various other indicator materials instead ofphenophthalein may be utilized with the proper electrode arrangement. Itshould be noted that this type of pH- E.M.F. relationship involves anexcess of hydrogen ions in the vicinity of the cathode and an excess ofhydroxyl ions adjacent the anode. Therefore, if the particular indicatorused changes between two different colors (e.g. from blue to pink)instead of from colorless to a color, a different color will be presentat each electrode. Thus, in such a case one of the electrodes should beremoved from the general vicinity of the mirror surface to pre venttwo-color interference.

An example of a substance useable in chamber 56 and having a pHvariation in response to temperature change is a solution of sodiumbicarbonate, diacetone alcohol, aqueous methanol, and an indicator suchas phenolphthalein. Such a solution could be composed of 3 parts sodiumbicarbonate, parts of diaectone alcohol, 50 parts of 10% aqueousmethanol solution, and /2 part of phenolphthalein.

Many other variations in the materials used, in the physical form of thesubstance and the like may be made in the structure illustrated in FIG.4. The essential factor is the presence of the color-changing materialin a uniformly dispersed manner over the front of the mirror surface tovary the reflectivity brightness from this mirror.

SECOND EMBODIMENT Referring now to FIG. 5, a second embodiment of theinventive mirror is there shown. Mirror 210 is mounted adjacent thewindshield 214 of an automobile as by connecting integral flanges 216 tothe frame 212 above the windshield. The size of the mirror may besubstantially larger than conventional rear view mirrors due to itsunique characteristics which prevent it from causing a permanent blindspot in the windshield. The mirror may be altered between asubstantially transparent nature (FIG. 5) to a substantially reflectivenature (FIG. 6) at the control of the driver by manipulation of asuitable foot switch or the like. When it is transparent, the driver hasclear vision of pedestrians, bicycles, approaching automobiles from sidestreets, etc., in front of the automobile by looking directly throughthe mirror (FIG. 5). When the driver causes the large mirror to becomereflective, automobiles, motorcycles, etc. around the rear of thevehicle are clearly observed (FIG.

6). In other words, the large mirror provides a much wider field ofeffective rear vision for the driver.

The construction of this mirror may be substantially as shown in FIG. 7.It may include a body portion 242 from which mounting flanges 216extend. Recess 244 is provided for insertion of a suitable lightbulb orother energy transmitting source 246. A frame 240 may be attached aroundthe periphery. The body includes a fluid chamber having an arcuate upperboundary 248. The structure is laminated to include a front glasssupport 260, a one-way mirror surface 262 (e.g. deposited chromium), anda light conducting, transparent layer having two spaced walls 266 and268 connected by peripheral rim 270 to define chamber 272 therein. Thischamber is filled with a variable-opacity substance responsive to anenergy source to become more opaque when activated. When the material inchamber 272 is transparent, light passes through the one-way mirrorsurface as indicated by the arrows in FIG. 8 according to well-knowprinciples concerning this type of mirror, i.e. it appears as a window.However, as is conventional with one-way mirrors, when light intensityincident to the back of the one-way mirror surface 262 is relativelyless than the light intensity incident to the front, the chromiumsurface acts as a mirror rather than as a window" and reflects the lightrather than transmitting it therethrough (FIG. 9).

With applicants inventive mirror, the area behind and adjacent theone-way rnirror surface 262 may be made dark or transparent to regulatethe incident light intensity from outside sources on the back of surface262 to cause it to alternatively be a window or a mirror as desired.This is done by filling chamber 272 behind the refiective surface with alight-responsive material that is reversibly opaque or transparent. FIG.9 illustrates this material in its opaque position as activated byenergy source 246. The light emitted from source 246 may, for example,be ultraviolet light to activate a mixture of water and 5% by weighttriethylamine. When this mixture is exposed to ultraviolet light, itchanges from transparent to turbid to substantially reduce lighttransmission therethrough. Since external light directed toward the rearof the mirror is not transmited through this layer, the light intensityincident to the front of surface 262 is relatively greater than thatbehind to cause surface 262 to become reflective.

The ultraviolet light may be conducted uniformly over the chamber (asindicated by the arrows in FIG. 7) due to the use of plastic materialshaving good light conducting qualities. Arcuate surface 248 aids in thisuniform light distribution through the plastic. An example of such aresin is polymethyl methacrylate. Many other plastic materials couldalso be used. Also, various structural and configurational variationsmay be made in the mirror shown to accommodate the particularapplication and type of energy source.

Another type of variable-opacity substance useful in the mirrorillustrated in FIGS. 5 through 9 is that which is converted reversiblyfrom the sol state to the gel state. These materials are usuallyresponsive to temperature changes. Further, this type of substance maybe used in a solid film state instead of a liquid contained in a chamberas previously described.

An example of the latter may be obtained by mixing a solution of (l) 10parts of methylpolyvinyl ether, (2) 5 parts of an emulsifying agent suchas glycololeate, salts of alkyl sulfonate, or neutral salts ofderivatives of naphthalene sulfonic acid, and (3) 6 parts of agar-agarin 300 part of water. This mixture is poured in a thin layer on a flatsupport and dried to obtain a film having variable opacity qualities. Itis then sandwiched between two suitable transparent layers such as glassor transparent plastic, or laminated to the glass layer 260 supportingthe one-way mirror surface. Another example of a sol-gel reversiblesubstance is an alkaline earth compound of polyacrylic acid in water, eg1% mixture of magnesium polyacrylic in water. The temperature of thereversible change of each particular substance will depend upon othermaterials present. Color changing substances may be used here also aswell as in the first embodiment. Thus, the above examples areillustrative only since materials experimented with presently and in thenear future will probably be just as useful, if not more so, as acomponent in the inventive concept described.

THIRD EMBODIMENT To produce a one-Way mirror flexible in characteristicsto adapt to both traflic and lighting conditions, the first twoembodiments described can be combined to obtain a mirror which can beboth alternately transparent and reflective (FIGS. 59) and which canenable control of a variable reflectivity brightness (FIGS. 1-4). Thestructure illustrated in FIG. may be used. In this structure, a one-Wayreflector surface 300 is coated on the back of a glass sheet 302.Variable opacity layer 304 is sandwiched between glass sheets 306 and308. Layer 304 is responsive to energy source 310 to become relativelyopaque or transparent as explained with respect to FIG. 9. In front ofsurface 300 and sandwiched between glass plates 302 and 316, is layer312 of a color-changing material. Layer 312 is responsive to energysource 314.

Layer 304 may be formed from the methylpolyvinyl ether compositiondescribed with respect to the apparatus of FIG. 9. Other substances maybe used. Layer 312 may be formed of a dye substance as described with respect to the layer 24 in FIG. 2. The concentration of the dye must becalibrated to cause its response to a high intensity light 314 insteadof automobile lights, etc. Suitable recesses 330 and 332 are provided inthe two sandwiches in back of, and in front of reflective layer 300 tochannel the light energy emitted from sources 310 and 314 down therespective sandwiches only. By utilizing independent controls overenergy sources 310 and 314, not only may the mirror surface 300 becontrolled between its transparent and reflective states, but also theglare or reflectivity brightness may be controlled simultaneously. Thus,on a dusky evening, layer 312 may be substantially colorless or a lightcolor, for example, and layer 304 may be alternated between opaque andtransparent, to allow alternate vision through the mirror, and to therear. On a sunny day on the other hand, layer 312 may be darkened to apink shade to reduce reflection glare, and may be alternated between areflective position and a transparent position by control of layer 304.

Energy sources 310 and 314 may be ordinary intensified light sources,may be infra-red sources to activate a substance particularly responsiveto such, may beultraviolet sources to activate a material particularlyresponsive. to ultraviolet wave lengths, may be radiant heat sources tocause temperature changes, may be conductive sources as illustrated inFIG. 4, or others. Also, each of these responsive layers may possess aconverting material capable of absorbing light and converting it intoheat to activate heat responsive material as explained previously.

It will be apparent to those in the art, that many possible combinationsmay be made with the mirror structures illustrated, such as the use ofmultiple color layers for color and opaqueness variations, or the use ofparticular substances to produce the color-changing oropaque-transparent effect, or the particular method of preparing thecolor-responsive or opaqueness responsive layer, and others. One exampleof such modifications is the coating of a mirror surface directly on theback of a thin layer of cast polymethyhnethacrylate which includesuniformly dispersed therein a light-responsive substance inserted duringits casting. Thus, the invention is not to be limited merely to theillustrative material, but only by the scope of the appended claims andthe equivalents thereto.

We claim:

1. An optically variable mirror, comprising: a supported one-way mirrorsurface comprising a partially reflective coating on a transparentsurface; said surface being generally transparent when the lightintensity incident to one side thereof is greater than the lightintensity incident to the opposite side, and said surface comprising areflective mirror surface when the light intensity incident to saidopposite side is greater than the light intensity incident to said oneside; a first substance adjacent said one side; first means to apply apredetermined energy potential to said first substance; said firstsubstance having an opacity variable with said 'rEW lied thereto suchthat the characterlstics OfSEtid surface may be atere etweentransparency and re ectivity; an a second substance acfiacent saidopposite side; second means to apply a predetermined type of energypotential to said second substance; said se n n r pable of colorvariations with te latter mentioned t e of reec ivity brightness from II I a samurramy ee varied.

2. An optically variable mirror, comprising: a supported one -way mirrorsurface comprising a partially refiective coating on a transparentsurface; said surface being generally transparent when the lightintensity inci dent to one side thereof is greater than the lightintensity incident to the opposite side, and said surface comprising areflective mirror surface when the light intensity incident to saidopposite side is greater than the light intensity incident to said oneside; a first substance adjacent said one side having an opacityvariable with a type of energy potential applied thereto such that thecharacteristics of said surface may be altered between transparency andreflectivity; a second color variable substance adjacent said oppositeside responsive to a type of energy potential applied thereto to changecolor, whereby the reflectivity brightness from said surface may bevaried; and a variable energy source for each of said substances capableof providing said types of energy, whereby the refiectivity-transparency characteristics may be controlled independentlyof the reflectivity brightness.

References Cited by the Examiner UNITED STATES PATENTS 2,710,274 6/ 1955Kuehl. 3,198,070 8/1965 Platzer et al 8877 References Cited by theApplicant UNITED STATES PATENTS 1,776,496 9/ 1930 Eiland.

2,632,045 3/1953 Sziklai.

2,710,274 6/ 1955 Kuehl.

2,776,598 1/ 1957 Dreyer.

2,824,235 2/1958 Hahn et al.

3,000,262. 8/ 1961 Rabinow et al.

FOREIGN PATENTS 737,765 9/ 1955 Great Britain.

JEWELL H. PEDERSEN, Primary Examiner.

JOHN K. CORBIN, Examiner.

1. AN OPTICALLY VARIABLE MIRROR, COMPRISING: A SUPPORTED ONE-WAY MIRRORSURFACE COMPRISING A PARTIALLY REFLECTIVE COATING ON A TRANSPARENTSURFACE; SAID SURFACE BEING GENERALLY TRANSPARENT WHEN THE LIGHTINTENSITY INCIDENT TO ONE SIDE THEREOF IS GREATER THAN THE LIGHTINTENSITY INCIDENT TO THE OPPOSITE SIDE, AND SAID SURFACE COMPRISING AREFLECTIVE MIRROR SURFACE WHEN THE LIGHT INTENSITY INCIDENT TO SAIDOPPOSITE SIDE IS GREATER THAN THE LIGHT INTENSITY INCIDENT TO SAID ONESIDE; A FIRST SUBSTANCE ADJACENT SAID ONE SIDE; FIRST MEANS TO APPLY APREDETERMINED ENERGY POTENTIAL TO SAID FIRST SUBSTANCE; SAID FIRSTSUBSTANCE HAVING AN OPACITY VARIABLE WITH SAID ENERGY POTENTIAL APPLIEDTHERETO SUCH THAT THE CHARACTERISTICES OF SAID SURFACE MAY BE ALTEREDBETWEEN TRANSPARENCY AND REFLECTIVITY; AND A SECOND SUBSTANCE ADJACENTSAID OPPOSITE SIDE; SECOND MEANS TO APPLY A PREDETERMINED TYPE OF ENERGYPOTENTIAL TO SAID SECOND SUBSTANCE; SAID SECOND SUBSTANCE BEING CAPABLEOF COLOR VARIATIONS WITH THE LATTER MENTIONED TYPE OF APPLIED ENERGYSUCH THAT THE REFLECTIVITY BRIGHTNESS FROM SAID SURFACE MAY BE VARIED.